1. Field of the Invention
The present invention relates to an antiglare layer used for restraining a screen glaring phenomenon attributable to highly fine pixels in a liquid crystal display device or the like, a film having the antiglare layer, and an optical element provided with the antiglare film.
2. Description of the Background Art
Hitherto, in a display device such as a liquid crystal display device, an antiglare layer (having an antiglittering property) has been disposed on the uppermost surface of a panel for preventing reflection of an outside environment by diffusing surface reflection light and restraining the regular reflection of outside light, thereby to improve the visibility of images. A generally known example of such an antiglare layer is a layer obtained by sandblasting, or by filling a resin layer having a thickness of from 5 to 10 xcexcm suitably with or transparent particles to impart a fine uneven structure on the surface thereof. In the case of highly fine liquid display device, however, when an antiglare layer such as described above is mounted thereon, a random intense-faint light is generated on the surface to aggravate the glaring, thereby inviting a problem of decrease in the image quality. In order to restrain such glaring, a method is proposed to dispose two or more of the aforesaid resin coats. Although such means can prevent the glaring phenomenon to some extent, the glaring phenomenon is not yet sufficiently restrained.
In addition, the aforementioned antiglare layer having a surface uneven configuration is effective in imparting the antiglare property in the case where an average crest-to-bottom interval is small to provide a dense structure, and the glaring phenomenon can be restrained to some extent. On the other hand, in the case of a structure having a dense surface uneven configuration, a phenomenon called xe2x80x9cwhitingxe2x80x9d occurs in which the surface looks whity by random reflection of outside light on the surface layer. This leads to a problem of decrease in the visibility of black color display particularly in a display device such as a liquid display device.
An object of the present invention is to provide an antiglare layer, which is capable of restraining the screen-glaring phenomenon while maintaining the antiglittering property and in which the whiting is observed to the least extent. A further object of the present invention is to provide a film having the antiglare layer and an optical element provided with the antiglare film.
As a result of repeated eager studies to solve the aforementioned problems of the prior art, the inventors have found out that the aforesaid object can be achieved by an antiglare layer having a structure described below, thereby completing the present invention.
Namely, the present invention is directed to an antiglare layer comprising at least one resin coat layer (a) containing particles and a resin coat layer (b) laminated on the resin coat layer (a), the resin coat layer (b) containing particles and having a surface uneven configuration, wherein an average particle size of the particles contained in the resin coat layer (b) is smaller than or equal to an average particle size of the particles contained in the resin coat layer (a).
In the present invention, the antiglare layer is made of a laminate where the lower layer contains particles having a larger average particle size than that of the particles contained in the upper layer. As a consequence, light diffusion can be effectively carried out in each layer, thereby restraining the glaring phenomenon attributable to diffusion of backlight in a liquid crystal display device.
Further, the antiglare layer of the present invention is designed in such a manner that the average particle size of the particles contained in the upper layer in the aforesaid laminate structure is smaller than or equal to the average particle size of the particles contained in the lower layer so that the particles with a smaller average particle size appear in the upper layer. Such a design mitigates the denseness of the surface uneven configuration to some extent, increases the crest-to-bottom interval of the surface uneven configuration to some extent, and reduces the average slant angle, whereby the whiting can be restrained. In the present invention, since the glaring is restrained by the above-mentioned laminate structure, the glaring on the surface is not so conspicuous to cause decrease in the image quality or in the visibility of the display screen as in the case of restraining the whiting by an antiglare layer with a single-layer structure.
Further, the resin coat layer (a) constituting the lower layer of the antiglare layer in the present invention serves to improve the surface rubbing resistance and hardness.
In the aforesaid antiglare layer, a surface roughness of the surface uneven structure of the resin coat layer (b) is preferably from 14 to 60 xcexcm, more preferably from 20 to 50 xcexcm, in terms of an average crest-to-bottom interval.
When the average crest-to-bottom interval is within the above-mentioned range, the antiglaring property and the antiwhiting property is obtained a good balance, hence it is preferable. The average crest-to-bottom interval is more preferably less than or equal to 30 xcexcm from the standpoint of the antiglittering property and the antiglaring property, and is preferably more than or equal to 30 xcexcm from the standpoint of the antiwhiting property. Here, the average crest-to-bottom interval is a value measured by using a contact-type surface roughness meter under a condition with a trace distance of 3 mm and a speed of 0.3 mm/s.
In the aforesaid antiglare layer, the average particle size of the particles contained in the resin coat layer (b) is preferably from 1 to 6 xcexcm, and the average particle size of the particles contained in the resin coat layer (a) is preferably from 2 to 10 xcexcm.
The average particle sizes of the particles contained in the resin coat layer (a) and the resin coat layer (b) are not specifically limited as long as the average particle size of the particles contained in the resin coat layer (b) is relatively smaller than or equal to the average particle size of the particles contained in the resin coat layer (a). However, if the average particle sizes of the particles are respectively within the above-mentioned ranges, the antiglittering property, the antiglaring property, and the antiwhiting property of the antiglare layer can be effectively exhibited. The average particle size of the particles contained in the lower resin coat layer (a) is more preferably from 3 to 5 xcexcm in order to obtain a light-diffusing effect more efficiently. The average particle size of the particles contained in the upper resin coat layer (b) is more preferably from 2 to 3 xcexcm in order to exhibit the aforesaid surface uneven configuration and to restrain the whiting to the minimum.
Further, the antiglare layer preferably includes a reflection-preventive layer disposed on a surface of the uneven configuration of the resin coat layer (b), the reflection-preventive layer having a refractive index smaller than that of the resin coat layer (b).
The reflection-preventive layer having a small refractive index can restrain the surface reflection and reduces the whiting more effectively.
In addition, the present invention is also directed to an antiglare film including the aforesaid antiglare layer disposed on one side or on both sides of a transparent substrate. The present invention is also directed to an optical element including the aforesaid antiglare layer or the aforesaid antiglare film disposed on one side or on both sides of the optical element.
The antiglare layer of the present invention can be used for various fields of use as an antiglare film disposed on a transparent substrate, for example, in an optical element.